A twist in the tail – Leeds researchers show how sperm wriggle

In a discovery with far-reaching potential for advances in infertility treatment, scientists at the University of Leeds have identified what makes sperm wriggle and swim. The answer lies in a protein called dynein. The scientists have taken the first photographs of individual molecules of dynein, also found in lungs, the nervous system and elsewhere in the human body. In an article in this week’s Nature, the researchers explain how the protein creates movement.

Project leader Dr Peter Knight said: “Dynein molecules are attached to tiny tubes within the sperm tail, and as the molecules change shape, they make the tubes slide back and forth causing the sperm’s tail to wriggle. We call these proteins molecular motors, as they work very much like engines, using fuel which the body creates from the food we eat to power movement.”

The scientists identified this movement by combining thousands of electron microscope images (taken by Dr Matt Walker) of individual molecules of the protein under different biochemical conditions – the first time such images had been obtained.

Lead researcher Dr Stan Burgess said: “Combining the images revealed the major shape change within the dynein molecule. That change is equivalent to the piston movement in a car’s engine which ultimately drives the wheels round.”

As well as making sperm wriggle, dynein also powers the cilia which push eggs along the Fallopian tubes towards the womb. The hard-working protein also helps clear the lungs of airborne debris and transports chemicals within our nervous system.

Head of the molecular contractility group, Professor John Trinick relates molecular motors to a railway network. “Our body is full of proteins which form tracks. Along these tracks, molecular motors are the locomotives, transporting a variety of cargoes to wherever they are needed.”

The protein plays a crucial role in a variety of gynaecological, bronchial, infertility and neurological disorders. It also ensures the body’s internal organs are the right way round: the body’s left-right axis, which places the heart on the left and the liver on the right, is caused by the activity of cilia during early development of the embryo.

Dr Peter Knight and colleagues at Leeds collaborated with a team in Japan which purify dynein from single-celled organisms which use the protein to swim around in ponds.

In 2000, the group showed the protein which carries chemicals round our nervous system – myosin V – ‘walking’ along protein tracks, the first time such a movement was identified. Identifying the movement of dynein confirms Leeds’ position at the forefront of this emerging area of research.